The present invention relates to a process for increasing process furnaces energy efficiency through gas turbine integration by using turbine exhaust gas, wherein a hydrocarbon feed is heated in a furnace. More in detail, the present invention relates to the increased energy efficiency of steam cracking by gas turbine integration.
U.S. Pat. No. 4,172,857 relates to a non-catalytic cracking process employing a pressurized riser-type thermal cracker heated by hot agglomerated ash particles circulated from a separate coal burning power producing combustion unit. Compressed air from a compressor passes through a conduit to coils of a heat exchanger and then passes to the main air supply conduit and to the branch conduit which supplies high velocity air to the recycle conduit means. The flue gases or combustion gases from the combustion unit pass upwardly through the outlet to the duct. The gases leaving the cyclone pass to the flue gas duct which carries the ash-free flue gases to the steam generator and a superheater. The gases then pass to the inlet of the gas turbine and to the heat exchanger. A steam turbine and an electric motor-generator are connected to the turbine and the compressor to assist in starting and the latter for generating electricity from excess power available after starting. The superheater and heat exchanger recover heat energy from the flue gases to provide steam and to preheat the liquid hydrocarbon feedstock and the air so that the flue gases are cooled. Boiler feed water introduced to the coils of the heat exchanger are preheated, and returned to a steam drum. Water from the steam drum is fed to a conventional heat exchanger heated by the cracked gases to form steam which is returned to the steam drum. Steam from the drum passes to the superheater coil, and superheated steam is discharged. The technology described here has a compressor compressing ambient air to a combined (catalyst) regeneration process/process heat supply. This compressor is driven by a turbine expanding a hydrocarbon gas from the process. The work produced/required by turbine and compressor are directly related to the process.
WO90/06351 relates to a process for inhibiting coke formation during the vaporization of heavy hydrocarbons by preheating such hydrocarbons in the presence of a small, critical amount of hydrogen in the convection section of a conventional tubular furnace. The technology described here is a technology to prevent coke formation in (steam) cracking furnaces and does not relate to a technology that is more energy efficient by the combining electricity production with steam cracking.
WO2010/077461 relates to a process to prevent coke formation and allows for processing of heavier hydrocarbon feed in cracking furnaces, comprising a process for cracking a hydrocarbon feedstream containing non-volatile components in a hydrocarbon cracking furnace having upper and lower convection heating sections within a flue of the furnace, a radiant heating section downstream of and connected to said lower convection heating section, a transfer line exchanger downstream of and connected to said radiant heating section, a furnace box containing furnace burners and said radiant heating section, and a vapor/liquid separator vessel connected between the upper and lower convection heating sections. The technology described here is a technology to prevent coke formation and allows for processing of heavier hydrocarbon feed in cracking furnaces and this reference does not describe a technology that is more energy efficient by the combining electricity production with steam cracking.
US patent application No 2013/001132 relates to a process and apparatus for producing olefins in a pyrolysis furnace employing TLEs to cool the pyrolysis gases, comprising injecting an amount of wetting fluid into the tubes of TLEs to keep the tube wall wetted thus to prevent coking, wherein the wetted-wall TLE can generate high pressure steam.
JPH0979506 relates to a method for injecting hydrazine in an exhaust heat recovery boiler for preventing the occurrence of pitting in the heat transfer tube of such an exhaust heat recovery boiler.
WO91/15665 relates to a method of adjusting the heat generation in a sulphate pulp process to correspond to the heat consumption by injecting excess steam into a gas turbine combustor or into the exhaust gas thereof.
U.S. Pat. No. 6,237,337 relates to retrofit equipment for reducing the consumption of fossil fuel by a power plant using solar insolation, wherein the power plant includes a waste heat boiler in the form of a series of heat exchanger coils and receiving hot exhaust gases. After exiting the boiler, the then heat-depleted exhaust gases are vented to the atmosphere. Vaporization of water in the heat exchange coils takes place in multiple stages, producing steam which is applied to a steam turbine coupled to a generator. The turbine expands the steam and drives a generator producing power from the generator and expanded steam from the turbine exhaust. A condenser condenses the expanded steam to condensate and the condensate is returned to the boiler to complete the water loop. Steam is applied to superheater coils producing superheated steam that is applied to the turbine.
Steam cracking, also referred to as pyrolysis, has long been used to crack various hydrocarbon feedstocks into olefins, preferably light olefins such as ethylene, propylene, and butenes. Conventional steam cracking utilizes a pyrolysis furnace which has two main sections: a convection section and a radiant section. The hydrocarbon feedstock typically enters the convection section of the furnace as a liquid (except for light feedstocks which enter as a vapour) wherein it is typically heated and vaporized by indirect contact with hot flue gas from the radiant section and by direct contact with steam. The vaporized feedstock and steam mixture is then introduced into the radiant section where the cracking takes place. The resulting products, including olefins, leave the pyrolysis furnace for further downstream processing, including quenching.
In an energy conversion process, for example operated by Lummus Technology, the steam cracker energy efficiency is increased through gas turbine integration wherein gas turbine flue gas (approx. 400-650° C., depending on gas turbine type, containing approximately 13-15% vol oxygen) is used as combustion air for the cracking furnaces. The gas turbine integration with ethylene plant comprises, inter alia, the use of turbine exhaust gas as a feed for combustion air distribution header.
Some aspects relating to this technology are: energy savings from combined heat and power (CHP) increase when more heat can be supplied to the process. The heat supply to the process (and thus energy savings potential) is limited by the combustion air requirements of the steam cracking furnaces, the size of the gas turbine is limited by the combustion air requirements in the furnaces, limiting possible scale advantages of larger gas turbines. This means that the operation scale of this technology is dictated by the intimate technical relationship between the steam cracking furnaces and the combined heat and power (CHP) resulting in some possible negative technical consequences.
This means that in such a construction a gas turbine trip has a significant disturbance on the cracking conditions resulting in consequences for the whole back end of the plant. This technology of integration results in additional steam production by the cracking furnaces. This limits the application potential of other energy savings options such as CHP plants or on sites with a balanced steam supply and consumption. Thus additional steam generated in the cracking furnaces will replace efficient steam generation from an on-site CHP plant resulting in less net savings.
An object of the present invention is to provide a method for increasing steam cracker energy efficiency through gas turbine integration in which method the furnace processes are run separately from the gas turbine processes.